Abstract: DESCRIPTION: (adapted from the application): This research project is designed to extend the Longitudinal Study of Aging Danish Twins (LSADT), a cohort-sequential study of elderly Danish twins. In 1995 these investigators completed 2401 (78% of those eligible) assessments on all participating twins aged 75 years and older; in 1997 they completed 2172 (79% of those eligible) assessments on all participating twins aged 73 years and older. In extending the LSADT, they propose to complete in-person interviews in 1999, 2001 and 2003 on all twins aged 70+ identified through the Danish Twin Registry (over 2,000 assessments at each wave and over 7,000 assessments during the renewal period). At each wave, the interview assessment will be based on the interview used in 1995 and 1997 and cover health, physical functioning, cognitive functioning depression symptomatology, social factors, lifestyle characteristics and quality of life. They will also supplement the self-report interview assessments with objective indicators of physical strength and agility, behavioral speed and pulmonary peak-flow. They will also collect from the participants, using Danish funds, biological material for future DNA analysis. The new data will be carefully checked and. archived together with data from the two previous surveys in 1995 and 1997 as well as with information from the comprehensive Danish health registers, including date of death and cause of death for all deceased twins (responders as well as nonresponders). This large and genetically informative longitudinal data set will provide us with an unprecedented opportunity to explore genetic and environmental influences on aging processes including physical decline, disease morbidity, and mortality.